Unless you have really good insulation, in hotter areas, your roof will absorb a lot of heat and that gets transferred to the attic and then to the rest of the house. One of the cheapest and best upgrades in hotter areas is to have an attic fan and vents to send the hot attic air outside.
Building science shows this is not true if you use A/C and have appropriate amount of ceiling insulation. Inadequate ceiling insulation is helped by this.
